August 30, 2014
Early in my years as a refractive surgeon performing incisional corneal refractive surgery, I learned that I could achieve the maximal effect of corneal incisions when they were made at 90° to the corneal plane. With the advent of femtosecond laser technology, surgeons now have the ability to create precise incisions anywhere from 30° to 150° relative to the corneal plane. This has allowed for a new means of titrating the effect because angulated femtosecond laser incisions are greater in length, provide an increased corneal healing interface and thus have less effect.
When I first started performing femtosecond astigmatic keratotomy (AK) in virgin eyes with astigmatism, I used maximal settings consisting of an 8-mm optical zone, paired 80° arc length incisions on the steep corneal meridian, a consistent depth of 75% of the thinnest pachymetry readings in the optical zone of treatment and an incision angle of 90°. This approach corrected astigmatism ranging from 2.3 D to 3.5 D (average of 2.8 D), but there were instances of poor predictability and occasional overcorrection.